Linear polymers of carbon monoxide with one or more .alpha.-olefins, in which the polymer component derived from carbon monoxide alternates with the other polymer components in units of the formula --(CO)--A--, wherein A represents a polymer component derived from the .alpha.-olefin, can be prepared by using a catalyst composition on the basis of
(a) a palladium compound, PA1 (b) a halogen monocarboxylic acid, and PA1 (c) a phosphorus bidentate ligand of the general formula R.sub.1 R.sub.2 P-R-PR.sub.3 R.sub.4, wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are similar or different aryl groups which may optionally be substituted with polar groups and R is a bivalent organic bridging group containing at least two carbon atoms in the bridge. PA1 (a) a palladium compound, PA1 (b) a halogen dicarboxylic acid, and PA1 (c) a phosphorus bidentate ligand of the general formula R.sub.1 R.sub.2 P-R-PR.sub.3 R.sub.4, wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are similar or different aryl groups which may optionally be substituted with polar groups and R is a bivalent organic bridging group containing at least two carbon atoms in the bridge.
Processes for the production of such polymers are illustrated by published European patent application Nos. 0,121,965; 0,181,014; and 0,222,454, which are incorporated by reference herein.
In the polymer preparation mentioned hereinbefore, both reaction rates and molecular weights of the polymers formed play an important role. On the one hand, it is desirable that the reaction rates achieved in the polymer preparation be as high as possible and on the other hand, the polymers will be more valuable with a view to their possible uses as their molecular weights are higher. Both reaction rates and molecular weights can be influenced by the temperature applied during polymerization. Unfortunately, the effects which the temperature has on the reaction rates and on the molecular weights are opposed to one another, in that, at otherwise similar reaction conditions, an increase in reaction temperature leads to increased reaction rates but decreased molecular weights of the polymers obtained. In actual practice, the trend is to conduct the polymerization at such a temperature that the polymers obtained have molecular weights which are sufficiently high for their intended uses and accept the reaction rates that go with that temperature.
In published European Patent No. 0,251,373 it was disclosed that high polyketone molecular weights could be produced at faster polymerization rates than known in the art by the combination of an increase in polymerization temperature and the use of specific bidentate phosphorus ligands.
In an investigation carried out by the Applicant into the above-mentioned catalyst compositions, it was recently found that their performance is greatly influenced by the amount of halogen monocarboxylic acid present in the catalyst composition. It was found that according as the concentrations of halogen monocarboxylic acid employed in the catalyst compositions are higher, the reaction rates that can be attained at one and the same reaction temperature are higher, and that the polymers obtained have higher molecular weights. This influence of the concentration of halogen monocarboxylic acid on reaction rates and on the molecular weights of the polymers is felt over a wide range of concentrations and it attains its maximum value at a halogen monocarboxylic acid concentration in the catalyst composition of about 20 mol per gram atom of palladium. Above this level of concentration, a further increase of the halogen monocarboxylic acid concentration will not lead to any further significant rise in reaction rates or molecular weights. In view of the favorable effect which a high halogen monocarboxylic acid concentration has both on the reaction rates and on the molecular weights of the polymers obtained, it has thus far been common practice in the preparation of the present polymers to employ a catalyst composition containing about 20 mol of halogen monocarboxylic acid per gram atom of palladium. Although from the stand point of process cost there can hardly be any objection to the application of a high halogen monocarboxylic acid concentration in the catalyst composition, since extremely small quantities of catalyst composition are sufficient for the preparation of the present polymers, the use of a catalyst composition with a high halogen monocarboxylic acid concentration involves another drawback. This drawback is connected with the fact that in the present polymer preparation a considerable portion of the catalyst composition used remains behind in the polymers. A relatively high halogen monocarboxylic acid concentration in the polymers can have an adverse effect on the stability of the polymers. This may lead to such problems as discoloring and decomposition during the working up in molten state of the generally high-melting polymers. It is true that the halogen monocarboxylic acid concentration in the polymers can be reduced by subjecting them to one or more washing treatments, but when practiced on a technical scale these will naturally involve considerable additional expenses.